The bus was bound to St. Louis from Memphis when a passenger became unruly. The female driver, who is cooperating with the investigation, bounced the passenger in Sikeston, Mo., then drove east to Charleston and abandoned the bus, according to Reuters.

Richmond said the driver, who has not been identified, is based in Memphis and has worked for Greyhound since 2004. She said the company has extensive training for its drivers in how to handle passengers, and that it would be acceptable to put a passenger off a bus if there's the feeling of a threat.

But Richmond said the driver should have notified Greyhound dispatch that she was leaving the bus. If she had done that, a new bus driver would likely have arrived within two hours, Richmond said.

"I think it's safe to say the protocol was not followed," Richmond told KSDK-TV in Memphis.

Greyhound didn't get a substitute driver to the scene until about eight hours later, the company said. Passengers offered refunds.